Im. Razumovskii et al., INVESTIGATION OF NI-63 DIFFUSION ALONG STATIONARY AND MOVING GRAIN-BOUNDARIES IN NB, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 212(1), 1996, pp. 45-50
Grain boundary diffusion of Ni-63 in high purity polycrystalline niobi
um has been studied in the temperature range 973-1258 K by the radiotr
acer serial sectioning technique. Since the grain size in the material
could not be completely stabilized by pre-diffusion heat treatment, s
ome part of the grain boundaries could migrate during the diffusion an
neals. The tracer penetration profiles were treated using the model of
diffusion in polycrystals containing both stationary and moving grain
boundaries developed in our previous work. Along with the grain bound
ary diffusivity, also the average velocity of moving grain boundaries
and the activation energy of boundary migration in Nb were determined
from the effect of boundary motion on the profile shape. Grain boundar
y diffusion of Ni in Nb is anomalously fast and exhibits an activation
energy of 155.2 kJ mol(-1). This behaviour is well consistent with th
at of Co diffusion in Nb studied previously and implies that diffusion
of both elements in Nb is governed by a combined atomic mechanism inv
olving both vacancies and interstitials.